Question

How do we see tap interfaces on underlying OVS bridge and how to check packet flow through the bridge interfaces?

  • 19 December 2018
  • 2 replies
  • 889 views

Hi,

As per the default configuration while deploying AHV, there is an underlying OVS bridge br0 that gets created

VMs deployed on AHV would send data through their virtual NICs which gets attached to tap0 or tap1 etc interface on br0.

1- How do we see these tap interfaces on br0? I do not see any tap interface listed in lab.

2- Should these tap interfaces be automatically created? If manual config is needed, how do we create it and link to the vNIC (that connects to VM)?

3- How do we do any packet captures or see data flow through these tap interfaces?

4- Why does the MAC address of VM gets listed on port 1 which is Uplink?

Attached some screenshots for reference:


2 replies

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wrt "1- How do we see these tap interfaces on br0? I do not see any tap interface listed in lab."

You can log into the AHV and type "ovs-vsctl show".

Under the "Bridge {bridgename}" section you should see you tapx information there listed as "Port 'tapx'" where x is your tap #.

Good luck!
Userlevel 1
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wrt 3: "3- How do we do any packet captures or see data flow through these tap interfaces?"

I came across this as I was looking for something myself:

"Tracing packets inside Open vSwitch"

from here: "http://docs.openvswitch.org/en/latest/topics/tracing/"

The web-site has a LOT of useful information... If I run across anything else that might apply to you I will post...

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